I was sure I had seen The Keep back in the 1980's because I was a pretty big Michael Mann fan (and I was a Michael Mann fan because, duh, 1980's, but mainly because of his show Crime Story).
But turns out, nope, I had NOT seen it, because if I had, I would have surely remembered how batshit crazy it is. I'm not going to even attempt to summarize the plot here, so I'll just say it involves World War II Nazis, a "keep" housing an ancient monster known as Radu Molasar, and Scott Glenn as a Greek (!), all accompanied by a totally anachronistic (though still pretty awesome) score by Tangerine Dream. And Scott Glenn isn't the only crazy casting. There's also Gabriel Byrne as a Nazi, and Ian McKellan as a Jewish historian.
The special effects in it are some of the worst I've ever seen in a big studio production, and I guess that's partly explained by the film's troubled production. It should also be noted that a good print of the movie is pretty hard to find. It's not on DVD -- and certainly not on Blu-ray -- and the streaming version I watched on Amazon Prime, and paid $2.99 for, is TERRIBLE. It looks like a second generation VHS recording of a LaserDisc print, which it probably is.
As terrible as The Keep is, I'd still love to be able to see a pristine print of it with a remastered soundtrack, because while it's terrible, it's also all kinds of audacious, and if I could actually see more of the movie, I think it might even win me over.